/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.search.aggregations;

import org.opensearch.LegacyESVersion;
import org.opensearch.common.Strings;
import org.opensearch.common.io.stream.NamedWriteable;
import org.opensearch.common.io.stream.StreamInput;
import org.opensearch.common.io.stream.StreamOutput;
import org.opensearch.common.util.BigArrays;
import org.opensearch.common.xcontent.XContentBuilder;
import org.opensearch.rest.action.search.RestSearchAction;
import org.opensearch.script.ScriptService;
import org.opensearch.search.aggregations.pipeline.PipelineAggregator;
import org.opensearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
import org.opensearch.search.aggregations.support.AggregationPath;

import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.IntConsumer;
import java.util.function.Supplier;

import static java.util.Objects.requireNonNull;

/**
 * An internal implementation of {@link Aggregation}. Serves as a base class for all aggregation implementations.
 *
 * @opensearch.internal
 */
public abstract class InternalAggregation implements Aggregation, NamedWriteable {
    /**
     * Builds {@link ReduceContext}.
     *
     * @opensearch.internal
     */
    public interface ReduceContextBuilder {
        /**
         * Build a {@linkplain ReduceContext} to perform a partial reduction.
         */
        ReduceContext forPartialReduction();

        /**
         * Build a {@linkplain ReduceContext} to perform the final reduction.
         */
        ReduceContext forFinalReduction();
    }

    /**
     * The reduce context
     *
     * @opensearch.internal
     */
    public static class ReduceContext {
        private final BigArrays bigArrays;
        private final ScriptService scriptService;
        private final IntConsumer multiBucketConsumer;
        private final PipelineTree pipelineTreeRoot;
        /**
         * Supplies the pipelines when the result of the reduce is serialized
         * to node versions that need pipeline aggregators to be serialized
         * to them.
         */
        private final Supplier<PipelineTree> pipelineTreeForBwcSerialization;

        /**
         * Build a {@linkplain ReduceContext} to perform a partial reduction.
         */
        public static ReduceContext forPartialReduction(
            BigArrays bigArrays,
            ScriptService scriptService,
            Supplier<PipelineTree> pipelineTreeForBwcSerialization
        ) {
            return new ReduceContext(bigArrays, scriptService, (s) -> {}, null, pipelineTreeForBwcSerialization);
        }

        /**
         * Build a {@linkplain ReduceContext} to perform the final reduction.
         * @param pipelineTreeRoot The root of tree of pipeline aggregations for this request
         */
        public static ReduceContext forFinalReduction(
            BigArrays bigArrays,
            ScriptService scriptService,
            IntConsumer multiBucketConsumer,
            PipelineTree pipelineTreeRoot
        ) {
            return new ReduceContext(
                bigArrays,
                scriptService,
                multiBucketConsumer,
                requireNonNull(pipelineTreeRoot, "prefer EMPTY to null"),
                () -> pipelineTreeRoot
            );
        }

        private ReduceContext(
            BigArrays bigArrays,
            ScriptService scriptService,
            IntConsumer multiBucketConsumer,
            PipelineTree pipelineTreeRoot,
            Supplier<PipelineTree> pipelineTreeForBwcSerialization
        ) {
            this.bigArrays = bigArrays;
            this.scriptService = scriptService;
            this.multiBucketConsumer = multiBucketConsumer;
            this.pipelineTreeRoot = pipelineTreeRoot;
            this.pipelineTreeForBwcSerialization = pipelineTreeForBwcSerialization;
        }

        /**
         * Returns <code>true</code> iff the current reduce phase is the final reduce phase. This indicates if operations like
         * pipeline aggregations should be applied or if specific features like {@code minDocCount} should be taken into account.
         * Operations that are potentially losing information can only be applied during the final reduce phase.
         */
        public boolean isFinalReduce() {
            return pipelineTreeRoot != null;
        }

        public BigArrays bigArrays() {
            return bigArrays;
        }

        public ScriptService scriptService() {
            return scriptService;
        }

        /**
         * The root of the tree of pipeline aggregations for this request.
         */
        public PipelineTree pipelineTreeRoot() {
            return pipelineTreeRoot;
        }

        /**
         * Supplies the pipelines when the result of the reduce is serialized
         * to node versions that need pipeline aggregators to be serialized
         * to them.
         */
        public Supplier<PipelineTree> pipelineTreeForBwcSerialization() {
            return pipelineTreeForBwcSerialization;
        }

        /**
         * Adds {@code count} buckets to the global count for the request and fails if this number is greater than
         * the maximum number of buckets allowed in a response
         */
        public void consumeBucketsAndMaybeBreak(int size) {
            multiBucketConsumer.accept(size);
        }

    }

    protected final String name;

    protected final Map<String, Object> metadata;

    private List<PipelineAggregator> pipelineAggregatorsForBwcSerialization;

    /**
     * Constructs an aggregation result with a given name.
     *
     * @param name The name of the aggregation.
     */
    protected InternalAggregation(String name, Map<String, Object> metadata) {
        this.name = name;
        this.metadata = metadata;
    }

    /**
     * Merge a {@linkplain PipelineAggregator.PipelineTree} into this
     * aggregation result tree before serializing to a node older than
     * 7.8.0.
     */
    public final void mergePipelineTreeForBWCSerialization(PipelineAggregator.PipelineTree pipelineTree) {
        if (pipelineAggregatorsForBwcSerialization != null) {
            /*
             * This method is called once per level on the results but only
             * has useful pipeline aggregations on the top level. Every level
             * below the top will always be empty. So if we've already been
             * called we should bail. This is pretty messy but it is the kind
             * of weird thing we have to do to deal with bwc serialization....
             */
            return;
        }
        pipelineAggregatorsForBwcSerialization = pipelineTree.aggregators();
        forEachBucket(bucketAggs -> bucketAggs.mergePipelineTreeForBWCSerialization(pipelineTree));
    }

    /**
     * Read from a stream.
     */
    protected InternalAggregation(StreamInput in) throws IOException {
        name = in.readString();
        metadata = in.readMap();
        if (in.getVersion().before(LegacyESVersion.V_7_8_0)) {
            in.readNamedWriteableList(PipelineAggregator.class);
        }
    }

    @Override
    public final void writeTo(StreamOutput out) throws IOException {
        out.writeString(name);
        out.writeGenericValue(metadata);
        if (out.getVersion().before(LegacyESVersion.V_7_8_0)) {
            assert pipelineAggregatorsForBwcSerialization != null
                : "serializing to pre-7.8.0 versions should have called mergePipelineTreeForBWCSerialization";
            out.writeNamedWriteableList(pipelineAggregatorsForBwcSerialization);
        }
        doWriteTo(out);
    }

    protected abstract void doWriteTo(StreamOutput out) throws IOException;

    @Override
    public String getName() {
        return name;
    }

    /**
     * Rewrite the sub-aggregations in the buckets in this aggregation.
     * Returns a copy of this {@linkplain InternalAggregation} with the
     * rewritten buckets, or, if there aren't any modifications to
     * the buckets then this method will return this aggregation. Either
     * way, it doesn't modify this aggregation.
     * <p>
     * Implementers of this should call the {@code rewriter} once per bucket
     * with its {@linkplain InternalAggregations}. The {@code rewriter}
     * should return {@code null} if it doen't have any rewriting to do or
     * it should return a new {@linkplain InternalAggregations} to make
     * changs.
     * <p>
     * The default implementation throws an exception because most
     * aggregations don't <strong>have</strong> buckets in them. It
     * should be overridden by aggregations that contain buckets. Implementers
     * should respect the description above.
     */
    public InternalAggregation copyWithRewritenBuckets(Function<InternalAggregations, InternalAggregations> rewriter) {
        throw new IllegalStateException(
            "Aggregation [" + getName() + "] must be a bucket aggregation but was [" + getWriteableName() + "]"
        );
    }

    /**
     * Run a {@linkplain Consumer} over all buckets in this aggregation.
     */
    public void forEachBucket(Consumer<InternalAggregations> consumer) {}

    /**
     * Creates the output from all pipeline aggs that this aggregation is associated with.  Should only
     * be called after all aggregations have been fully reduced
     */
    public InternalAggregation reducePipelines(
        InternalAggregation reducedAggs,
        ReduceContext reduceContext,
        PipelineTree pipelinesForThisAgg
    ) {
        assert reduceContext.isFinalReduce();
        for (PipelineAggregator pipelineAggregator : pipelinesForThisAgg.aggregators()) {
            reducedAggs = pipelineAggregator.reduce(reducedAggs, reduceContext);
        }
        return reducedAggs;
    }

    /**
     * Reduces the given aggregations to a single one and returns it. In <b>most</b> cases, the assumption will be the all given
     * aggregations are of the same type (the same type as this aggregation). For best efficiency, when implementing,
     * try reusing an existing instance (typically the first in the given list) to save on redundant object
     * construction.
     *
     * @see #mustReduceOnSingleInternalAgg()
     */
    public abstract InternalAggregation reduce(List<InternalAggregation> aggregations, ReduceContext reduceContext);

    /**
     * Signal the framework if the {@linkplain InternalAggregation#reduce(List, ReduceContext)} phase needs to be called
     * when there is only one {@linkplain InternalAggregation}.
     */
    protected abstract boolean mustReduceOnSingleInternalAgg();

    /**
     * Return true if this aggregation is mapped, and can lead a reduction.  If this agg returns
     * false, it should return itself if asked to lead a reduction
     */
    public boolean isMapped() {
        return true;
    }

    /**
     * Get the value of specified path in the aggregation.
     *
     * @param path
     *            the path to the property in the aggregation tree
     * @return the value of the property
     */
    public Object getProperty(String path) {
        AggregationPath aggPath = AggregationPath.parse(path);
        return getProperty(aggPath.getPathElementsAsStringList());
    }

    public abstract Object getProperty(List<String> path);

    /**
     * Read a size under the assumption that a value of 0 means unlimited.
     */
    protected static int readSize(StreamInput in) throws IOException {
        final int size = in.readVInt();
        return size == 0 ? Integer.MAX_VALUE : size;
    }

    /**
     * Write a size under the assumption that a value of 0 means unlimited.
     */
    protected static void writeSize(int size, StreamOutput out) throws IOException {
        if (size == Integer.MAX_VALUE) {
            size = 0;
        }
        out.writeVInt(size);
    }

    @Override
    public Map<String, Object> getMetadata() {
        return metadata;
    }

    /**
     * The {@linkplain PipelineAggregator}s sent to older versions of OpenSearch.
     * @deprecated only use these for serializing to older OpenSearch versions
     */
    @Deprecated
    public List<PipelineAggregator> pipelineAggregatorsForBwcSerialization() {
        return pipelineAggregatorsForBwcSerialization;
    }

    @Override
    public String getType() {
        return getWriteableName();
    }

    @Override
    public final XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
        if (params.paramAsBoolean(RestSearchAction.TYPED_KEYS_PARAM, false)) {
            // Concatenates the type and the name of the aggregation (ex: top_hits#foo)
            builder.startObject(String.join(TYPED_KEYS_DELIMITER, getType(), getName()));
        } else {
            builder.startObject(getName());
        }
        if (this.metadata != null) {
            builder.field(CommonFields.META.getPreferredName());
            builder.map(this.metadata);
        }
        doXContentBody(builder, params);
        builder.endObject();
        return builder;
    }

    public abstract XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException;

    @Override
    public int hashCode() {
        return Objects.hash(name, metadata);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        if (obj == this) {
            return true;
        }

        InternalAggregation other = (InternalAggregation) obj;
        return Objects.equals(name, other.name) && Objects.equals(metadata, other.metadata);
    }

    @Override
    public String toString() {
        return Strings.toString(this);
    }

    /**
     * Get value to use when sorting by this aggregation.
     */
    public double sortValue(String key) {
        // subclasses will override this with a real implementation if they can be sorted
        throw new IllegalArgumentException("Can't sort a [" + getType() + "] aggregation [" + getName() + "]");
    }

    /**
     * Get value to use when sorting by a descendant of this aggregation.
     */
    public double sortValue(AggregationPath.PathElement head, Iterator<AggregationPath.PathElement> tail) {
        // subclasses will override this with a real implementation if you can sort on a descendant
        throw new IllegalArgumentException("Can't sort by a descendant of a [" + getType() + "] aggregation [" + head + "]");
    }
}
